1. Field of the invention
The present invention relates to an improved system and method for automatically controlling a vehicle speed to a desired cruise speed having a fail safe function.
2. Background of the Art
Various types of systems and methods for automatically controlling a vehicle speed to desired cruise speed without operation of an accelerator pedal have been proposed.
One of the automatic cruise speed controlling systems is exemplified by a Japanese Patent Application First Publication No. sho 60-42131 published on Mar. 6, 1985.
In a vehicle in which the automatic cruise speed controlling system disclosed in the above-identified Japanese Patent Application Publication is mounted, the speed of the vehicle at which a driver desires to cruise is set through a set/cruise switch. The opening angle of a throttle valve is adjusted so that the vehicle speed coincides with the set cruise speed. With the system, it is convenient for the driver to run the vehicle at the set cruise speed without operation of the accelerator pedal.
In such an automatic cruise speed controlling system, a control unit having a microcomputer is provided in which a throttle actuator is controlled in accordance with the contents of a command signal. The command signal is derived from any one of several command switches including the set/cruise switch, and release switches which release cruise speed control.
However, as recent trends dictate, countermeasures against software and hardware troubles due to high level noises are demanded.